The present invention relates to a bone fixation screw system The present invention also provides methods of utilization of bone fixation screw systems. More particularly an embodiment of the present invention relates to a compression hip screw system for strong and stable internal fixation for a variety of intertrochanteric, subtrochanteric and basilar neck fractures as well as compression screw systems for superacondylar or "T" condylar fractures about the distal femur.
Bone fixation screw systems are used often for internal fixation of fractures of the hip bone and distal femur. The bone structure typically will have first and second bone sections separated from one another by a fracture interface. The bone second section is the major portion of the bone structure which includes the femoral shaft. A surgeon will drill a transsectional bore into the bone. The bore will go through all of the bone second section and then will typically only partially penetrate into the bone first section. A front portion of the bore in the bone first section is then tapped to provide a female thread therein.
The surgeon then inserts into the bore a lag screw (a specialized form of a bone screw). The lag screw is typically machined from cold worked stainless steel due to strength and biological requirements. The lag screw has an intergral male thread at its forward end. A shank of the lag screw extends rearward from the male threads and passes through the bore in both the first and second bone sections. The lag screw is then rotated by the surgeon to threadably attach the lag screw to the bone first section.
The surgeon then inserts a barrel into a rear end of the bore in the second bone section. Typically the barrel will have an internal diameter with opposed flats that match longitudinal flats on the lag screw. Alignment of the flats on the lag screw and barrel prevent the lag screw from rotating. Therefore the lag screw cannot be inadvertently released from the first bone section.
The barrel is integrally connected with a side plate. The side plate is angled from the barrel. The side plate extends along a side of the second section of the bone parallel to a major axis of the bone second section. The surgeon then attaches the side plate to the second section (femoral shaft) of the bone via a series of mounting screws. The lag screw on its rear end has an internal bore previously tapped with a female thread. A shank of a compression screw is threadably connected with the rear end of the lag screw. A head of the compression screw is seated against a counter bore seat of the barrel. Torquing the compression screw causes the lag screw to be pulled rearward and places the first bone section in compression against the fracture interface. The amount of compression utilized will be determined by the surgeon.
After the fracture has sufficiently healed it is sometimes desirable to remove the lag screw. To remove the lag screw the compression screw is threadably released from the lag screw. The side plate must then be removed from the side of the bone by removal of its mounting screws. As the side plate is removed, the barrel will be rearwardly pulled out of the bore in the second bone section.
In the healing process the bone will grow into the female threads that were tapped in the first and second bone sections, locking the lag screw in position. Therefore the lag screw cannot be simply rotated to threadably release the lag screw from the bone first section. To release the lag screw a trephine is fitted over the lag screw. The trephine is used to cut a core of bone surrounding the lag screw to allow release of the lag screw. A more detailed review of the present state of the art can be gained by a review of the surgical technique of Frank R. Ebert M.D. Baltimore Md., as described in Biomet Brochure Y-BMT-415/031595/M .RTM.1995 Biomet, Inc. Warsaw Ind. 46580.
Although excellent results have been achieved with the above noted process it would be desirable to modify the lag screw removal process. The above noted lag screw removal process requires the cutting of additional bone tissue, after a prior healing process. Furthermore the side plate and barrel must be removed before the lag screw can be removed.
It would be desirable to provide a bone fixation screw system wherein the lag screw would have sufficient strength and wherein the lag screw could be removed without the use of a trephine. It would also be desirable to have a bone fixation screw system which allows removal of the lag screw without removal of the barrel and side plate.